Process control systems, such as distributed or scalable process control systems like those used in utility power, water, oil refinement, wastewater or other processes, typically include one or more process controllers communicatively coupled to each other, to at least one host or operator workstation, and to one or more plant devices via analog, digital or combined analog/digital buses. The plant devices, which may be, for example, valves, valve positioners, switches, transmitters (e.g., temperature, pressure and flow rate sensors), perform functions within the process such as opening or closing valves and measuring process parameters.
A process controller typically receives signals indicative of process measurements made by the field devices (plant devices) and/or other information pertaining to the field devices, uses this information to implement a control routine, and generates control signals that are sent to the field devices to control the operation of the process. Information from the field devices and the process controller is typically made available via one or more applications that are executed by a workstation operator to perform a desired function with respect to the process, such as viewing the current state of a process, modifying the operation of a process, etc. A control loop typically refers to the overall control process including the measurement of process parameters and modifying the operation of the process parameters to effectuate one or more control processes, such as regulation of temperature, pressure, flow rate, etc. A process plant may have any suitable number of control loops based on an interaction between various field devices that is needed to adequately regulate a control process. As a result, the field devices may communicate with the process controller as well as with one another to ensure efficient process control.
Traditionally, control signals and/or the communications between field devices has been implemented using one or more wires or buses. More recently, wireless industrial automation protocols have been introduced to facilitate these communications. One such wireless industrial automation protocols used in the process control industry is the wireless Highway Addressable Remote Transmitter (HART) Communication Foundation protocol, referred to generally as the WirelessHART protocol. Generally speaking, the WirelessHART protocol utilizes a time synchronized, self-organizing, and self-healing mesh architecture, and supports operation in the 2.4 GHz Industrial, Scientific, & Medical (ISM) band using IEEE 802.15.4 standard radios. New field devices may be designed that are compatible with the WirelessHART protocol, or existing wired field devices may be retrofitted with an adapter to provide WirelessHART communication functionality.
Using WirelessHART protocols, control processes may be carried out wirelessly between the process controller and one or more field devices. However, some functions, such as firmware updates, software updates, calibration, configuration, etc., typically utilize physical, wired connections to the field devices, which may be performed with a field communicator that connect to a field device with a cable. Because the electronic connectors used to facilitate wired communications need to be protected from conditions in a plant environment, the electronic connectors are often protected by a cover, such as an end cap, for example, that may be removed to provide a user appropriate access for a wired connection.
Requiring a user to directly and physically connect to a field device presents several issues. First, the end cap or other covering may not be properly resealed upon completion of the task at hand, which may then expose the connector to the plant's harsh environmental conditions. Second, some plant processes may need to be stopped to provide access to a field device, since wired connections may require a user to be dangerously close to operating equipment.
Additionally, when connecting to the field device, the field communicator and the field device typically communicate using the same industrial automation protocol implemented by the field device, such as a wired HART protocol, for example. As a result, field communicators often use hardware and software components specifically designed for industrial automation protocol communications, thereby adding to their complexity and cost. Since field communicators typically only communicate using industrial automation protocols, the ability to access other data from the plant automation network is also limited.
Finally, although wireless field devices provide a more convenient means for facilitating process control by eliminating wires to carry control signals, initially setting up, or provisioning, new field devices into a preexisting plant network can be an arduous task. This is because most field devices are designed to perform plant related automation tasks, and therefore do not typically implement a user interface to allow a user to easily enter the requisite network authentication information.
As a result, maintaining the convenience of wireless plant control while eliminating the need to connect field communicators to field devices presents several challenges.